Polarization insensitive semiconductor optical amplifier

Abstract

A polarization insensitive semiconductor optical amplifier (SOA) is provided. The SOA includes an active waveguide, a passive waveguide, and a taper coupler for coupling optical energy from the passive waveguide into the active waveguide, wherein the taper coupler has width W varying relative to position along a main axis z of propagation of the SOA in proportion to the minimum value of 1/C TE 01 (z) 1/C TM 01 (z), where C TE 01 (z) represents the coefficient of energy coupling between a fundamental mode and a first order mode for the transverse electric polarization as a function of the position z, and C TM 01 (z) represents the coefficient of energy coupling between a fundamental mode and a first order mode for the transverse magnetic polarization as a function of the position z.

1. A polarization insensitive semiconductor optical amplifier (SOA), comprising an active waveguide, a passive waveguide, and a taper coupler for coupling optical signal energy from said passive waveguide into said active waveguide, said taper coupler having width W in a lateral x direction transverse to a z direction of a main axis of propagation of said SOA, said width W varying relative to position in said z direction, wherein a rate of variation (dw/dz) of said width W relative to the position in said z direction is in proportion to the minimum value of 1/C TE 01 (z) and 1/C TM 01 (z), where C TE 01 (z) represents the coupling coefficient between a fundamental mode and a first order mode for the transverse electric polarization at a position along the main axis, and C TM 01 (z) represents the coupling coefficient between a fundamental mode and a first order mode for the transverse magnetic polarization at that position. 
     
     
       2. The semiconductor optical amplifier of  claim 1  further comprising a separate confinement layer between said passive waveguide and said active waveguide. 
     
     
       3. The semiconductor optical amplifier of  claim 2  wherein said separate confinement layer includes an epitaxially grown semiconductor that is not intentionally doped. 
     
     
       4. The semiconductor optical amplifier of  claim 3  wherein said separate confinement layer includes a layer of Indium-Gallium-Arsenide-Phosphide (InGaAsP) having a bandgap wavelength of 1.05 μm. 
     
     
       5. The semiconductor optical amplifier of  claim 1  wherein said taper coupler has minimum width no smaller than a minimum lithographic feature size of a contact lithography process for making said semiconductor optical amplifier. 
     
     
       6. The semiconductor optical amplifier of  claim 5  wherein a width of said taper coupler is at least 1 μm at a smallest point. 
     
     
       7. The semiconductor optical amplifier of  claim 1  wherein said taper coupler and said passive waveguide are separated by a separate confinement layer disposed in a plane parallel to a main axis of propagation of light within said semiconductor optical amplifier. 
     
     
       8. The semiconductor optical amplifier of  claim 1  wherein said passive waveguide comprises a diluted fiber waveguide for coupling optical energy in a direction of at least one of to an optical transmission fiber and from an optical transmission fiber. 
     
     
       9. The semiconductor optical amplifier as claimed in  claim 1  wherein an axial direction of the taper coupler lies within a plane defined by said x direction and z direction and is oriented at an angle away from said z direction and away from said x direction. 
     
     
       10. The semiconductor optical amplifier as claimed in  claim 9  wherein the angle is seven degrees away from said z direction. 
     
     
       11. A polarization insensitive semiconductor optical amplifier (SOA), comprising an active waveguide, a passive waveguide, and a taper coupler for coupling optical signal energy from said passive waveguide into said active waveguide, said taper coupler having width W in a lateral x direction transverse to a z direction of a main axis of propagation of said SOA, said width W varying relative to position in said z direction, wherein said active waveguide includes a plurality of first quantum wells interleaved with a plurality of second quantum wells, said first quantum wells having tensile strain and said second quantum wells having compressive strain. 
     
     
       12. A polarization insensitive optical unit comprising a first waveguide and a second waveguide having a common direction of propagation (z), and a taper coupler for coupling optical signal energy from said first waveguide into said second waveguide, said taper coupler having width W in a lateral x direction transverse to said z direction, said width W varying relative to position in said z direction, wherein a rate of variation (dw/dz) of said width W relative to the position in said z direction is in proportion to the minimum value of 1/C TE 01 (z) and 1/C TM 01 (z) where C TE 01 (z) represents the coupling coefficient between a fundamental mode and a first order mode for a light wave having transverse electric polarization at a position along the main axis, and C TE 01 (z) represents the coupling coefficient between a fundamental mode and a first order mode for the transverse magnetic polarization at that positions. 
     
     
       13. The optical unit as claimed in  claim 12  wherein said first and second waveguides and said taper coupler consist entirely of portions of a monolithic multilayer structure. 
     
     
       14. The optical unit as claimed in  claim 13  wherein said multilayer structure includes semiconductor materials. 
     
     
       15. The optical unit as claimed in  claim 14  wherein said semiconductor materials are selected from the group consisting of III-V semiconductors. 
     
     
       16. The optical unit as claimed in  claim 15  wherein said semiconductor materials are selected from the group consisting of phosphide semiconductors. 
     
     
       17. The optical unit as claimed in  claim 12  wherein at least one of said first waveguide and said second waveguide includes an optoelectronic receiver. 
     
     
       18. The optical unit as claimed in  claim 12  wherein at least one of said first waveguide and said second waveguide includes a p-i-n photodiode receiver. 
     
     
       19. The optical unit as claimed in  claim 12  wherein at least one of said first waveguide and said second waveguide includes a photodiode. 
     
     
       20. The optical unit as claimed in  claim 12  wherein at least one of said first waveguide and said second waveguide includes an optoelectronic modulator. 
     
     
       21. The optical unit as claimed in  claim 12  wherein at least one of said first waveguide and said second waveguide includes an optoelectronic transmitter. 
     
     
       22. The optical unit as claimed in  claim 12  wherein an axial direction of the taper coupler lies within a plane defined by said x direction and z direction and is oriented at an angle away from said z direction and away from said x direction. 
     
     
       23. The optical unit as claimed in  claim 22  wherein the angle is seven degrees away from said z direction. 
     
     
       24. A polarization insensitive lateral taper coupler operable to couple optical signal energy from a first waveguide into a second waveguide, the first waveguide and the second waveguide having a common direction of propagation (z), said taper coupler having width W in a lateral x direction transverse to said z direction, said width W varying relative to position in said z direction, wherein a rate of variation (dw/dz) of said width W relative to the position in said z direction is in proportion to the minimum value of 1/C TE 01 (z) and 1/C TM 01 (z) where C TE 01 (z) represents the coupling coefficient between a fundamental mode and a first order mode for a light wave having transverse electric polarization at a position along the main axis, and C TM 01 (z) represents the coupling coefficient between a fundamental mode and a first order mode for the transverse magnetic polarization at that positions. 
     
     
       25. The lateral taper coupler as claimed in  claim 24  wherein said lateral taper coupler consists entirely of portions of a monolithic multilayer structure. 
     
     
       26. The lateral taper coupler as claimed in  claim 25  wherein said multilayer structure includes semiconductor materials. 
     
     
       27. The lateral taper coupler as claimed in  claim 26  wherein said semiconductor materials are selected from the group consisting of III-V semiconductors. 
     
     
       28. The lateral taper coupler as claimed in  claim 27  wherein said semiconductor materials are selected from the group consisting of phosphide semiconductors. 
     
     
       29. The lateral taper coupler as claimed in  claim 24  wherein said width w of said lateral taper coupler in said lateral direction x is no smaller than a minimum lithographic feature size of a contact lithography process for making said lateral taper coupler. 
     
     
       30. The lateral taper coupler as claimed in  claim 29  wherein said lateral taper coupler is etched to a width no smaller than 1 μm at a smallest point. 
     
     
       31. The lateral taper coupler as claimed in  claim 24  wherein an axial direction of the taper coupler lies within a plane defined by said x direction and z direction and is oriented at an angle away from said z direction and away from said x direction. 
     
     
       32. The lateral taper coupler as claimed in  claim 31  wherein the angle is seven degrees away from said z direction.